The immune system distinguishes self from nonself and defends self by excluding nonself from the body. The immune system has a skillful regulatory function to minimize the attack on the self cells (components), and autoimmune diseases are considered to be developed due to collapsed regulatory function. The autoimmune disease is largely divided into systemic autoimmune diseases and organ-specific autoimmune diseases. Of these, the organ-specific autoimmune disease refers to the diseases associated with chronic inflammations in particular organs or tissues (brain, liver, eye, arthrosis) and considered to be caused by an immune response to an autoantigen specific the organ (autoimmune response). Representative diseases include multiple sclerosis (brain, spinal cord) and rheumatoid arthritis (arthrosis). These diseases have many common aspects such as deviation of Th1/Th2 immune balance toward Th1, and the like, even when the disordered organs are different, and the treatment methods are basically the same.
NKT cell, which is one kind of lymphocytes constructing the immune system, has an NK cell receptor and a T-cell receptor, and has been identified as a new lymphocyte group showing different characteristics from those of other lymphocyte series (T, B, NK cells). One of the functions characterizing the NKT cell is that it recognizes, as an antigen, glycolipid (α-galactosylceramide) presented to CD1d belonging to major histocompatibility complex (MHC) class I molecules, thereby abundantly producing cytokines such as IL-4 and the like.
Noting such function of NKT cell, a therapeutic drug for autoimmune diseases comprising α-galactosylceramide as an active ingredient has been proposed (WO 98/044928). Since IL-4 produced by activation of NKT cells shows an autoimmune disease-suppressive action, autoimmune diseases are expected to be treated by activating NKT cells by administration of α-galactosylceramide.